Electrodeposition of bright copper



3,322,657 ELECTRODEPOSETION OF BRIGHT COPPER Karl-Wilhelm Sassenroth, Dusseldorf, Georg Jansen,

Neuss (Rhine), and Robert Brugger, Bernhausen, near Stuttgart, Germany, assignors to Langbein-Pfanhauser Werke A.G., Neuss (Rhine), Germany No Drawing. Filed May 11, 1964, Ser. No. 366,628 6 Claims. (Cl. 204-52) This invention relates to the electrodeposition of copper from acid electrolytes, and more particularly to the deposition of bright smooth copper coatings free from pores from acid electrolytes.

Acid copper plating solutions normally yield dull or semi-lustrous deposits with relatively poor throwing power. Known addition agents are capable of improving brightness, leveling ability, freedom from pores, or ductility of the deposit, but a combination of these properties is not readily obtained by known addition agents, and it is difficult to maintain satisfactory performance of a copper plating bath with respect to all the factors enumerated. It is generally necessary to provide an acid copper plating solution with at least one addition agent for each of the properties to be influenced. The multiple addition agents are lost from the plating bath by drag-out or decomposition at different rates, and their presence is not usually capable of being determined by simple chemical or physical analysis.

An object of the invention is the provision of an acid copper electroplating bath containing a source of copper ions and a source of hydrogen ions as is conventional, and producing copper electrodeposits which combine the afore-rnentioned desirable properties to a Very high extent with the use of a very small number of addition agents, preferably no more than two.

Another object is the provision of a new combination of addition agents for copper plating solutions which has good levelling effects, prevents the formation of pores due to hydrogen bubbles, and does not embrittle the copper deposits formed.

Yet another object is the provision of brighteners which are insensitive to relatively high concentrations of impurities in the plating bath, and thus permit operation over extended periods without requiring purification of the electrolyte.

We have found that the above objects are achieved by a combination of addition agents one of which is an N tetrahydropyranyl-Z substituted amide of a car-boxylic or thiocarboxylic acid. A wide variety of such amides may be used in acid copper plating solutions in amounts as low as 0.2 millimole per liter. The porosity and ductility of the deposits is not unfavorably influenced when the concentration of such primary addition agents is raised to their limit of solubility or 0.01 mole per liter whichever is lower.

The primary addition agents of the invention are of the formula wherein X is either oxygen or sulfur, R is hydrogen or the radical of propane-w-sulfonic acid, and R may be any one of a large number of radicals to complete the struc- 3,322,657 Patented May 30, 1967 ture of an N-tetrahydropyranyl-Z substituted carboxylic or thiocarboxylic acid amide, and more specifically that of an N-tetrahydropyranyl-2-substituted urea or thiourea, as will hereinafter become apparent.

The primary addition agents of the invention in which R is hydrogen are prepared in yields of 20 to percent from 2,3-dihydropyrane and amides corresponding to the brightening compounds to be produced in the presence of catalytic amounts of hydrogen chloride according to a method presented to the 139th meeting of the American Chemical Society, 1961, by A. I. Speziale, K. W. Ratts, and G. I. Marco (J. Org. Chem., 26, 4311 14, 1961; C. A., 56, 14218, 1962; Angew. Chem., 1961 (73), 497). The compounds prepared in this manner readily react with propane sultone to form the corresponding N-n-propane-w-sulfonic acids.

According to the dual substituents R and X, the primary addition agents of the invention are of four general types in each of which the nature of the substituent R is not particularly critical as long as it does not reduce the solubility of the compound below the lower limit of effectiveness.

The compounds of the first type in which X is oxygen and R is hydrogen are preferably employed in concentrations between 0.5 millimole per liter and their upper limit of solubility or approximately five millimoles 'per liter, whichever is lower. No further desirable changes in deposit properties are achieved by exceeding the concentration of five millimoles per liter where solubility is adequate.

The following compounds are representative of the first type of primary addition agent:

( l) N- tetrahydropyranyl-Z) -acetamide (2) N (tetrah ydropyranyl-Z -propionamide N tetrahydropyranyl-Z -butyramide N- tetrahydropyranyl-Z -benzarnide N- tetrahydropyranyl-Z) -p-toluamide N- (tetrahydropy-ranyl-Z -nicotinamide N- tetrahydropyranyl-Z) -picolinamide N- (tetrahydropyranyl-Z N '-acetylurea N- (tetrahydrop yranyl-Z -Ncarbethoxyurea 10) N- tetrahydropyranyl-Z) -N'-phenylsulfonylurea 1 1) N- (tetrahydropyranyl-Z) -N'-nitrourea 12) N- (tetrahydropyranyl-Z) I'-carboxyurea The second type of primary addition agent differs from the first type by the substitution of a radical for the hydrogen atom in position R of the compounds of the first type. All compounds of the first type enumerated above for the sake of illustration may be converted to the second type by reaction with propane sultone. The twelve compounds so obtained are readily soluble, and their brightening elfects increase over a wider range of concennations than those of the first type of primary brighteners. The second type of primary addition agents is preferably employed at concentrations of 0.5 millimole per liter and higher, and their favorable effects increase up to a concentration of 0.01 mole per liter.

The third type of primary addition agents according to the invention differs from the first type :by substitution of sulfur for the oxygen in position X. The thiamides of the third type are more eifective than the corresponding substituted amides of the first type at equal concentrations, and are preferably employed over a range of 0.2 millimole to five millimoles per liter or to their limit of solubility whichever is lower. The following compounds are representative of the third type:

The fourth type of primary addition agent of the invention differs from the second type by the presence of sulfur in position X of the formula, and representative compounds of the fourth type are obtained by reaction of propane sultone with each of the compounds (13) to (27) enumerated hereinabove. The compounds of the fourth type are employed over the same range of concentrations as those of the second type.

The primary brightening agents of the invention are highly effective in both types of acid copper plating solutions presently in commercial use, namely the sulfate type and the fluoborate type. Their use with electroplating solutions of these types is illustrated by the following eX- amples, but it will be understood that the invention is not limited to the examples.

Example 1 A copper plating solution was prepared from Copper sulfate, cryst., grams per liter 200 Sulfuric acid, C.P., grams per liter 0 N(tetrahydropyranyl-2)-nicotinamide, moles per liter 0.0009

Copper was deposited from the solution under the following conditions: Temperature, C. 22 to 26 Cathode current density, amps. per square foot (average) 45 Agitation (cathode movement), meters per min. 2 to 8 Example 2 A copper plating electrolyte was prepared from Copper fluoborate, grams per liter 250 Fluob-oric acid, grams per liter 3O N-(tetrahydr-opyranyl-2)-N-acetylurea, moles per liter 0.0012 The following operating conditions were maintained during plating:

Temperature, C. 22 to 28 Cathode current density, amps. per square foot average Agitation (cathode movement), meters per min.

The deposits formed were fully bright over an actual cathode current density range of 6.3 to 81 amps. per

square foot as determined on a bent brass sheet electrode, and had a good leveling effect.

Closely similar effects were achieved with the other compounds of the first type enumerated above sub (1) to (12).

Example 3 The composition and operating conditions of a copper plating solution were as follows:

Copper sulfate, cryst., grams per liter 200 Sulfuric acid, C.P., grams per liter 60 N (tetrahydropyranyl 2) N (n propane-wsulfonic acid)-acetamide, moles per liter 0.003

Temperature, C. 20 to 28 Cathode current density, amps. per sq. ft 45 Agitation (cathode movement), meters per min. 2 to 8 The coating produced were bright, pore-free, and of very high ductility. Scratches in the base metal having a depth of 40 microns were practically completely leveled when the average thickness of the copper coating reached 20 microns.

Closely similar results were obtained under otherwise comparable conditions when the brightening agent used was replaced by the other products of the reaction between propane sultone and the compounds of the first type listed sub (1) to (12).

Example 4 A copper plating solution of the composition listed below was used under the indicated operating conditions:

Copper fiuoborate, grams per liter 300 Fluoboric acid, grams per liter 40 N-(tetrahydropyranyl 2)-N-(n-propane-w-sulfonic acid)-N-carbethoxyurea, moles per liter 0.004 Temperature, C. 20 to 28 Cathode current density, amps. per sq. ft. 63 Agitation (cathode movement), meters per min. 2 to 8 The copper coatings produced were fully bright over an actual cathode current density range of 5.4 to amps. per square foot as determined with a bent brass sheet cathode, and had a very good leveling effect. Closely similar results were obtained with the other brightening compounds referred to in Example 3.

Example 5 Mirror bright copper deposits free from pores and of very good ductility were produced from an electrolyte of the following composition under the operating conditions listed:

Copper sulfate, cryst., grams per liter 200 Sulfuric acid, C.P., grams per liter 60 N (tetrahydropyranyl 2) p thiotoluamide,

moles per liter 0.0006 Temperature, C. 22 to 26 Cathode current density, amps per sq. ft. average 45 Agitation (cathode movement), meters per min. 2 to 8 The copper plate was fully bright over an actual cathode current density range from 2.7 to 72 amps. per square foot. Scratches in the base metal having a depth of 40 microns were practically leveled when the average coating thickness reached 15 microns. Equimolccular amounts of the other compounds of the third type listed above under numbers (13) to (27) gave corresponding results.

Example 6 Mirror bright copper deposits were obtained from a fluoborate electrolyte having the following composition, and operated under the listed conditions:

Copper fluoborate, grams per liter 250 Fluoboric acid, grams per liter 40 N-(tetrahydropyranyl 2)-N-carboxythiourea,

moles per liter 0.001

Temperature, C. 20' to 26 Cathode current density, amps. per sq. ft. average 54 Agitation (cathode movement), meters per min. 2 to 8 A sulfate type copper plating bath was prepared and operated as follow-s:

Copper sulfate, cryst., grams per liter Sulfuric acid, C.P., grams per liter 60 N-(tetrahydropyranyl 2)N-(n-propane-w-sul fonic acid)-N'-acetylthiourea, moles per liter 0.0015 Temperature, C. 20 to 28 Cathode current density, amps. per sq. ft. 45 Agitation (cathode movement), meters per min. 2 to 8 The coatings produced were mirror bright from 1.8 to 72 amps. per square foot of actual cathode current density. They were ductile and free from visible pores. irregularities in the base metal having a depth of 40 microns were completely leveled when the average thickness of the deposit reached 15 microns.

Similarly favorable results were obtained with the other reaction products of propane sultone with the compounds of the third type listed sub (13) to (27). Peak performance was obtained from the several compounds at concentrations varying between 0.001 and 0.003 mole per liter.

Example 8 Very ductible copper electrodeposits having good leveling action and being mirror bright were obtained from a fiuoborate bath as follows:

Copper fluoborate, grams per liter 250 Floboric acid, grams per liter 30 N-(tetrahydropyranyl 2) -N-(n-propane-w-sulfonic acid)-N-ally1 thiourea, moles per liter 0.0024 Temperature, C. 20 to 28 Cathode current density, amps per sq. ft. average -1 54 Agitation (cathode movement), meters per min. 2 to 8 posits can be obtained, particularly at operating temperatures of 25 to 50 C., and by further improving the leveling effects of the bath.

The secondary addition agents are amines of the formula or corresponding ammonium salts of the formula 1 R4-N+\R2 A wherein R is tetrahydropy-ranyl (I) or tetrahydrofuryl C32 CH- R and R are hydrogen, lower alkyl, phenyl, 2-carboxyphenyl, 4-hydroxyphenyl, 4-sulfophenyl, p-diphenyl, Z-pyridyl, 6,8-disulfo-2-naphthyl, the sulfo radical -SO H, or a radical (CH ),,SO H wherein n is an integer not greater than 4, and preferably 3 or 4, and R is lower alkyl. When R is different from lower alkyl, R is a member of the last mentioned group different from R A" may be the anion of any organic or inorganic acid. The nature of the anion is generally irrelevant since the desirable effects of the ammonium salts are due entirely to the cationic component.

The following compounds are representative of the secondary addition agents of the invention:

( 1) N-2-tetrahydropyrany1N-methylamine (2) N-2-tetrahydropyranyl-N-2-carboxyphenylamine (3) N-2-tetrahydropyranyl-N-Z-carboxyphenyl-N- methylamine (4) N-Z-tetrahydropyranyl-N-4-hydroxyphenylamine 5 N-2-tetrayhdropyranyl-N-w-sulfo-n-butylamine (6) N-Z-tetrahydropyranyl-N-w-sulfo-n-propylamine (7) N-Z-tetrahydropyranyl-aniline (8) N-2-tetrahydropyranyl-N-2-pyridyl-N-w-sulfo-npropylamine (9) N-2-tetrahydropyranyl-N-6,8-disulfo-2-napthyl- N-w-sulfo-n-propylamine 10) N-Z-tetrahydropyranyl-N-2-carboXyphenyl-N-wsulfo-nbutylamine 1 1) N-Z-tetrahydropyranyl-N-trimethylammonium sulfate l2) N-2-tetrahydropyranyl-N-4-hydroXyphenyl-N- dimethylammonium chloride 13 N-2-tetrahydrofuryl-N-methylamine (14) N-2-tetrahydrofuryl-N-4-sulfonphenyl-N-wsulfo-n-propylamine 15) N-Z-tetrahydrofuryl-N-2-pyridyl-N-w-sulfo-nbutylamine 16) N -2-tetrahydrofuryl-N-4-hydroxyphenyl-N- dimethylammonium chloride 17) N-Z-tetrahydropyranyl-N-p-diphenylyl-amine 18) N-2-tetrahydropyranyl-N-sulfo-amine The secondary addition agents of the invention may be added to the copper plating solutions described in EX- amples 1 and 8 in amounts of 0.05 to 2.0 grams per liter. The effects produced vary with concentration in the same manner as described hereinabove with reference to the primary brightening or addition agents. The range of permissible operating conditions is increased by the secondary agents, brightness and brightness range are improved, particularly at higher temperatures.

All secondary addition agents of the invention are beneficial to the several types of plating solutions enumerated in the examples, and may be combined with all the primary addition agents specifically described hereinabove. The following example is merely typical of the results obtained.

Example 9 A sulfate type copper plating bath was prepared as described in Example 7, but the solution additionally contained as a secondary addition agent 0.003 mole per liter of N-Z-tetrayhdropyranyl N-2-pyridyl-N-w-sulfo-npropylamine. Without loss of brightness, the bath could be operated at an average current density of 90 amps. per square foot, and the temperature could be permitted to rise to 50 C. Ductility and freedom from pores were not impaired, and leveling was improved as indicated by disappearance of irregularities in the base metal at an average thickness lower than that of Example 7.

It will be appreciated that the acid copper sulfate and copper fluoborate electrolytes described in Examples 1 to 9 are entirely conventional in composition except for the brightening agents of the invention, and that the operating conditions employed are not unusual. The effects of the constituents in these solutions are well known, and those skilled in the art will find that variations in the concentrations of copper salts and free acids in these electrolytes affect the bright deposits of the invention in a manner analogous to the effects produced in the absence of the brightening agents.

The temperature of the solutions is not critical. No effort was made in the plating runs reported on in the examples to hold the temperature within specific limits. The brightening agents of the invention are effective at temperatures as low as 10 C. or as high as 50 C. It is not usually necessary to employ copper sulfate or copper fluoborate plating solutions outside these extreme temperatures. An operating temperature between 10 C. and 50 C. is readily maintained without heating or cooling of the electrolyte under the ambient conditions of temperature prevailing in almost any plating plant.

The coatings produced do not lose their brightness or smoothness as their thickness increases. Coatings having a thickness of one millimeter (0.04 inch) are still fully bright, ductile, and dense.

The addition agents of the invention are chemically stable in acid copper electrolytes when obviously unstable substituents are avoided. They are consumed at a low rate during current passage through the electrolyte, and this rate is readily determined for a given plating installation so that replenishment of brightening agents may be based on measurements of ampere hours of current passed.

Bright deposits can be obtained with the brightening agents of the invention up to cathode current densities of about 90 amps. per square foot without agitation. Current densities much higher than 90 amps. per square foot are entirely practical with suitably rapid relative movement of electrolyte and plated object.

The brightening agents of the invention are relatively insensitive against contaminating ions such as those of lead, zinc, nickel, divalent and trivalent iron, and even hexavalent chromium. Copper plating solutions of the invention thus produce electrodeposits of the desired properties when made up of commercial chemicals of the grades normally employed in the electroplating industry without requiring purification by chemical treatments, electrolysis at low current density, or the like.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not limited thereto, but is to be construed broadly and restricted solely by the scope of the appended claims.

What is claimed is:

1. An aqueous acid copper plating electroylte containing as a primary brightening agent an effective amount of an N-(tetrahydropyranyl-Z) amide of a carboxylic acid dissolved in said electroylte; and as a secondary brightening agent an effective amount of an amine of the formula R1 RzN or an ammonium ion of the formula t R4N+/-R;

in said formulas R being tetrahydropyranyl or tetrahydrofuryl; R and R being hydrogen, lower alkyl, phenyl, Z-carboxyphenyl, 4-hydroxyphenyl, 4-sulfophenyl, poiphenylyl, 2-pyridyl, 6,S-disulfo-Z-naphthyl, or a sulfonic acid radical (CH ),,SO H wherein n is an integer not greater than 4; said R being different from said R when said R is different from lower alkyl; and R being lower alkyl.

2. An aqueous acid copper plating electroylte containing as a primary brightening agent an effective amount of an N-(tetrahydropyranyl-Z) amide of a thiocarboxylic acid dissolved in said electroylte; and as a secondary brightening agent an effective amount of an amine of the formula t RZN/ or an ammonium ion of the formula R1 R -N+ R in said formulas R being tetrahydropyranyl or tetrahydrofuryl; R and R being hydrogen, lower alkyl, phenyl, 2-carboxyphenyl, 4-hydroxyphenyl, 4-sulfophenyl, p-diphenylyl, 2-pyridyl, 6,8-disulfo-2-naphthyl, or a sulfonic acid radical (CH ),,SO H wherein n is an integer not greater than 4; said R being different from said R when said R is different from lower alkyl; and R being lower alkyl.

3. An aqueous acid copper plating electroylte containing as a primary brightening agent an effective amount of an N-(tetrahydropyranyl-Z -N-(propane-w-sulfonic acid) amide of a carboxylic acid dissolved in said electrolyte; and as a secondary brightening agent an effective amount of an amine of the formula or an ammonium ion of the formula R1 R4N+/R1| in said formulas R being tetrahydropyranyl or tetrahydrofuryl; R and R being hydrogen, lower alkyl, phenyl, Z-carboxyphenyl, 4-hydroxyphenyl, 4-sulfophenyl, p-diphenylyl, Z-pyridyl, 6,8-disulfo-2-naphthyl, or a sulfonic acid radical (CH SO H wherein n is an integer not greater than 4; said R being different from said R when said R is different from lower alkyl; and R being lower alkyl.

4. An aqueous acid copper plating electrolyte containing as a primary brightening agent an effective amount of an N-(tetrahydropyrnnyl-Z) N-propane-w-sulfonic acid amide of a thiocarboxylic acid dissolved in said electrolyte; and as a secondary brightening agent an effective amount of an amine of the formula a or an ammonium ion of the formula R1 R4N+/R2 in said formulas R being tetrahydropyranyl or tetrahydrofuryl; R and R being hydrogen, lower alkyl, phenyl, Z-carboxyphenyl, 4-hydroxyphenyl, 4-su-1fophenyl, p-diphenylyl, Z-pyridyl, 6,8-disulfo-2-naphthyl, or a sulfonic acid radical (CH fiSO H wherein n is an integer not greater than 4; said R being different from said R when said R is different from lower alkyl; and R being lower alkyl.

5. An aqueous acid copper plating electrolyte comprising copper sulfate or copper fluoborate as a source of copper ions, sulfuric acid or fiuoboric acid as a. source of hydrogen ions, an effective amount of a primary brightening agent of the formula wherein X is oxygen or sulfur, R is hydrogen or the radical -CH -CH SO H, and R is lower alkyl, phenyl, pyridyl, or a radical of the formula NHR", wherein R" is hydrogen, lower alkenyl, lower alkanoyl, carboxy, car-bo-(lower)-alkoxy, phenylsulfonyl, nitro, formyl, cyano, or phenyl; and as a secondary brightening agent an effective amount of an amine of the formula or an ammonium ion of the formula R1 R4-N+/-R9 acid radical (CH fiSO H wherein n is an integer not greater than 4; said R being different from said R when said R is different from lower alkyl; and R being lower alkyl.

6. A method of producing a bright, smooth, pore-free, and ductile copper coating on a conductive object which comprises making said object a cathode in an aqueous electrolyte containing copper sulfate or copper flu-oborate as a source of copper ions, sulfuric acid or fiuoboric acid as a source of hydrogen ions, a primary brightening agent, and a secondary brightening agent, said sources and said agents being dissolved in said solution, said primary agent being a N-(tetrahydropyranyl-2) amide of a carboxylic or thiocarboxylic acid, or an N(tetrahydropyranyl-2-)-N-(propane-w-sulfonic acid) amide of a carboxylic or thiocar-boxylic acid, said secondary brightening agent being an amine of the formula R1 zN s or an ammonium ion of the formula R1 R N+ R a being tetrahydropyranyl or tetrahydrofuryl; R and R being hydrogen, lower alkyl, phenyl, Z-carboxyphenyl, 4-hydroxyphenyl, 4-sulfophenyl, p-diphenylyl, Z-pyridyl, 6,8-disulfo-2-naphthyl, or a sulfonic acid radical (CH SO H wherein n is an integer not greater than 4; said R being different from said R when said R is different from lower alkyl; and R being lower alkyl, the concentration of said primary brightening agent in said electrolyte being between 0.2 and ten millimoles per liter, the concentration of said secondary brightening agent in said electrolyte being between 0.05 and 2.0 grams per liter, and the temperature of said electrolyte being between 10 C. and 50 C.

in said formulas R FOREIGN PATENTS 4/1964 Germany.

JOHN H. MACK, Primary Examiner. G. KAPLAN, Assistant Examiner. 

6. A METHOD OF PRODUCING A BRIGHT, SMOOTH, PORE-FREE, AND DUCTILE COPPER COATING ON A CONDUCTIVE OBJECT WHICH COMPRISES MAKING SAID OBJECT A CATHODE IN AN AQUEOUS ELECTROLYTE CONTAINING COPPER SULFATE OR COPPER FLUOBORATE AS A SOURCE OF COPPER IONS, SULFURIC ACID OR FLUOBORIC ACID AS A SOURCE OF HYDROGEN IONS, A PRIMARY BRIGHTENING AGENT, AND A SECONDARY BRIGHTENING AGENT, SAID SOURCES AND SAID AGENTS BEING DISSOLVED IN SAID SOLUTION, SAID PRIMARY AGENT BEING A N-(TETRAHYDROPYRANYL-2) AMIDE OF A CARBOXYLIC OR THIOCARBOXYLIC ACID, OR AN N-(TETRAHYDROPYRANYL-2-)-N-(PROPANE-W-SULFONIC ACID) AMIDE OF A CARBOXYLIC OR THIOCARBOXYLIC ACID, SAID SECONDARY BRIGHTENING AGENT BEING AN AMINE OF THE FORMULA 